934
FXUS63 KLOT 302339
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
639 PM CDT SUN AUG 30 2026
KEY MESSAGES
- PERIODIC SHOWER AND STORMS THROUGH THE EARLY PART OF THE WEEK,
THOUGH THERE WILL AMPLE DRY PERIODS.
- HOTTER AND MORE HUMID CONDITIONS BUILD THROUGH MIDWEEK.
DISCUSSION
ISSUED AT 231 PM CDT SUN AUG 30 2026
A SHORTWAVE DISTURBANCE OVER NORTHEASTERN IOWA WILL CONTINUE TO
DRIVE SHOWERS AND EMBEDDED THUNDERSTORMS EASTWARD THROUGH EARLY
THIS EVENING, WITH THE GREATEST COVERAGE EXPECTED NORTH OF
I-80. WHILE A 20% CHANCE FOR LIGHTNING REMAINS, POOR MID-LEVEL
LAPSE RATES ACROSS NORTHERN ILLINOIS SHOULD LIMIT THUNDERSTORMS
TO ISOLATED COVERAGE.
FOLLOWING THE EASTWARD DEPARTURE OF THIS SHORT-WAVE IMPULSE
THIS EVENING, A SOUTHWESTERLY LOW-LEVEL JET WILL RAMP UP AGAIN
OVERNIGHT, WITH THE CORE EXPECTED TO RESIDE OVER IA
NORTHEASTWARD INTO SOUTHERN WI. ASSOCIATED ISENTROPIC UPGLIDE
(WARM AIR ADVECTION) MAY THUS FOSTER MORE ISOLATED TO SCATTERED
SHOWERS AND THUNDERSTORMS LATE TONIGHT INTO EARLY MONDAY
MORNING. THEREAFTER, CAPPING IS LIKELY TO CURTAIL THE THREAT OF
CONVECTION FOR MUCH OF THE AREA INTO MONDAY AFTERNOON. HOWEVER,
ANOTHER SHORT-WAVE IMPULSE IS PROGGED TO TRANSLATE EASTWARD
TOWARDS NORTHWESTERN IL LATE IN THE DAY, AND THUS MAY ACT AS THE
IMPETUS FOR ISOLATED TO WIDELY SCATTERED AFTERNOON DEVELOPMENT
ACROSS NORTHWESTERN IL AFTER 2 PM. SHOULD THIS ACTIVITY OCCUR,
~40 KT OF MID-LEVEL WESTERLY FLOW COULD SUPPORT A FEW STRONGER
STORMS ACROSS NORTHWESTERN IL LATE IN THE AFTERNOON. CONFIDENCE
REMAINS LOW WITH THE EXTENT OF THIS THREAT.
CONVECTIVE TRENDS CONTINUE TO BE OF LOW CONFIDENCE MONDAY NIGHT
INTO TUESDAY MORNING. NEVERTHELESS, LOW (20-30%)CHANCES FOR
STORMS CONTINUE DUE TO THE PERSISTENT WARM-AIR ADVECTION PATTERN
IN COMBINATION WITH ADDITIONAL SMALLER SCALE PERTURBATIONS
LIKELY TO TRANSITION EASTWARD ACROSS SOUTHERN WI THROUGH THE
MID-LEVEL RIDGE AXIS. THE BETTER FOCUS FOR STORMS MAY REMAIN IN
SOUTHERN WI, BUT AT THIS TIME, CANNOT RULE OUT STORMS AS FAR
SOUTH AS THE I-80 CORRIDOR. THE SPC DAY 3 SEVERE OUTLOOK (FOR
TUESDAY) PLACES MOST AREAS NORTH OF I-80 IN A LEVEL 1 OF 5
THREAT. SO, WHILE CONFIDENCE IN THE COVERAGE OF STORMS REMAINS
LOW INTO TUESDAY MORNING, THE METEOROLOGICAL ENVIRONMENT WILL BE
SUPPORTIVE OF A CONDITIONAL THREAT FOR STRONG STORMS.
OUTSIDE OF THE THREAT OF STORMS THROUGH TUESDAY MORNING,
TEMPERATURES AND HUMIDITY LEVELS WILL BE ON THE RISE THROUGH
MID-WEEK AS THE AIRMASS UNDER THE EXPANSIVE MID/UPPER-LEVEL
RIDGE CONTINUES TO WARM. WE ANTICIPATE HIGH TEMPERATURES IN THE
UPPER 80S MONDAY, THE LOW 90S TUESDAY AND THE LOW TO MID 90S
WEDNESDAY. IN SPITE OF US BEING PAST THE PEAK TIMING FOR
EVAPOTRANSPIRATION, LIMITED MIXING UNDER AN INVERSION CENTERED
NEAR 850 MB SHOULD KEEP DEW POINTS IN THE LOW TO MID 70S DURING
PEAK HEATING, PARTICULARLY ON TUESDAY AND WEDNESDAY, RESULTING
IN PEAK HEAT INDICES IN THE 100 TO 105 RANGE.
RELIEF FROM THE HEAT LOOKS PLAUSIBLE LATER IN THE WEEK AS A
BACKDOOR COLD FRONT SAGS SOUTHWARD INTO THE AREA. HOWEVER, THIS
LOOKS TO COME AT THE EXPENSE OF A PERIOD OF MORE ACTIVE WEATHER
(A PERIOD OR TWO OF THUNDERSTORMS, SOME POSSIBLY STRONG) AT THE
END OF THE WEEK. THE SPECIFICS SUCH AS THE TIMING OF THE FRONT
AND BEST POTENTIAL FOR THUNDERSTORMS REMAIN A BIT UNCLEAR AT
THIS POINT, BUT STORM CHANCES BEGIN TO RAMP UP ACROSS OUR AREA
LATE WEDNESDAY NIGHT INTO THURSDAY.
KJB
AVIATION /00Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 639 PM CDT SUN AUG 30 2026
MAIN AVIATION FORECAST CONCERNS FOR THIS TAF PERIOD ARE TIMING
POTENTIAL PERIODS OF SHRA/TSRA.
AT ISSUANCE TIME, A CONVECTIVELY-ENHANCED MID-LEVEL DISTURBANCE
WAS TRACKING EAST ACROSS NORTHEAST IL/SOUTHERN LM. WHILE SOME
SUBSIDENCE WAS OCCURRING IMMEDIATELY BEHIND THIS FEATURE AND
RESULTING IN A BREAK IN THE LIGHT RAIN/SHOWERS, ADDITIONAL LIGHT
RAIN/EMBEDDED TS WAS OCCURRING WITHIN PERSISTENT SOUTHWEST FLOW
ACROSS PARTS OF IA/WI AND NW IL. MID-LEVEL LAPSE RATES WEAKEN
WITH EASTWARD EXTENT, SO NOT EXPECTING TS TO MAKE IT INTO THE
TERMINALS WITH ANY SIGNIFICANT COVERAGE, THOUGH IT DOES APPEAR
THAT A PERIOD OF SCATTERED SHRA/-RA WILL LINGER ACROSS THE AREA
THROUGH MID-EVENING.
THOUGH CONFIDENCE IN FORECAST DETAILS DECREASES LATER TONIGHT
INTO MONDAY, CURRENT GOES WATER VAPOR IMAGERY AND CAM FORECAST
TRENDS DO SUPPORT A COUPLE ADDITIONAL PERIODS OF BETTER
SHRA/TSRA POTENTIAL. THE FIRST IS AFTER 3-4 AM INTO MID-MORNING
MORNING, AND THE OTHER IS MID-LATE AFTERNOON MONDAY AS INDIVIDUAL
MID-LEVEL WAVES PROPAGATE THROUGH THE REGION. HAVE MAINTAINED
PROB30 MENTIONS FOR TSRA FOR BOTH, WITH STEEPER MID-LEVEL LAPSE
RATES FORECAST. OTHERWISE, VFR CONDITIONSARE EXPECTED THROUGH
THE PERIOD CEILINGS GENERALLY ABOVE 7-8 KFT. THE EXCEPTION MAY
BE BRIEF MVFR VIS REDUCTIONS IN HEAVIER CONVECTIVE SHRA/TS.
WINDS WILL REMAIN LIGHT SOUTH OVERNIGHT, BECOMING SOUTHWEST
AFTER DAYBREAK MONDAY. GUSTS AROUND 20 KT APPEAR LIKELY FROM
MID/LATE MORNING INTO THE AFTERNOON, EASING WITH THE APPROACH OF
SUNSET.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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